Modern computer operating systems and graphics programs require a pointing device for controlling the position of a cursor on the computer display. Likewise, handheld devices such as personal information managers and cell phones would also benefit from the inclusion of such a pointing device. For desktop PCs, the most successful pointing device is the “mouse”. A mouse is a hand held object that is moved over a flat surface near the keyboard to control the motion of a cursor on the computer display. The direction and distance over which the mouse is moved determines the direction and distance the cursor moves on the display. A conventional mouse provides a rigid object that a user can move with great precision. For a desktop computer, the mouse provides a satisfactory solution to the pointing problem. On the occasion when the workspace is not large enough to provide a path over which the mouse can move and accommodate a desired cursor movement on the screen, the user simply picks up the mouse and recenters the mouse in the workspace.
While the mouse has provided a satisfactory solution to the pointing device problem in the desktop PC market, a similarly successful device is not available for hand-held devices such as cellular telephones. These devices lack a sufficiently large flat surface near the keypad or screen over which a mouse can be moved. In addition, the need to carry a separate pointing device makes the mouse less than ideal for these applications. Hence, some other form of pointing device is needed when using these devices.
A pointing device for use in these environments must solve the problem of moving a cursor quickly and accurately. In addition, the device must operate in an intuitive fashion that a novice user can comprehend without extensive instruction. In addition, the pointing device must operate in a limited workspace and fit within the form factor of the hand held device. Finally, the usual constraints of low cost, low power consumption and high reliability must also be met.
In the case of laptop computers, there are two dominant solutions to the pointing device problem in the marketplace, the Synaptics capacitive TouchPad™ and the IBM TrackPoint™. Other companies make versions of these devices with similar functionality. Both of these devices fall far short of satisfying the above requirements. The TrackPoint™ is a small button that is typically placed in the center of the laptop keyboard. The button may be moved in a manner analogous to a “joy stick” by applying a lateral force to the top of the button with a finger. Unfortunately, the button can only move a small amount; hence, the displacement of the button cannot be mapped directly into a displacement in the cursor position on the computer display. Instead, the button displacement controls the direction and speed with which the cursor moves. The accuracy with which a user can position the cursor using this type of velocity control is significantly less than that achieved with a conventional mouse. This limitation is particularly evident in tasks that require small, precise movements such as drawing in a computer graphics program. In addition, this type of pointing device does not provide the button functionality.
The TouchPad™ is a blank rectangular pad, 50 to 100 mm on a side, typically placed below the keyboard of most laptops. The device senses the position of a finger on the surface of the rectangle relative to the edges of the device. This sensing is accomplished by measuring the capacitance changes introduced by a user finger on a series of electrodes beneath an insulating, low-friction material.
Like the TrackPoint™, the TouchPad™ also suffers from lack of precision. It is inherently difficult to measure the capacitive changes introduced by the user, who is at an unknown potential relative to the circuit. Furthermore, the contact area of the user's finger is relatively large. Hence, to provide an accurate measurement of the finger position, the device must determine some parameter such as the center of the contact area between the finger and the pad. Unfortunately, the contact area varies in size and shape with the pressure applied by the user. Therefore, such determinations are, at best, of limited precision. In practice, users are unable to repeatably execute precise movements.
There are also difficulties arising from false signals when the user inadvertently touches the pad with a finger or a wrist. In some devices, the “clicking” function of a conventional mouse is implemented by tapping on the pad. As a result, such inadvertent activation during typing causes the cursor to jump to a new location in the middle of the typing operation and the text being inserted at the new location.
In previously filed U.S. patent application Ser. No. 10/723,957, which is hereby incorporated by reference, a puck-based pointing device that overcomes many of the problems described above is taught. The pointing device utilizes a puck that moves in a defined field of motion when a user applies pressure to the puck via the user's finger. When the user releases the puck, a set of springs returns the puck to its centered position within the field of motion. The position of the puck and the pressure on the puck are determined by electrodes in the device. The position information is used to position a cursor on the display screen. Software on the attached device translates the motion of the puck during the time the user's finger is pressing on the puck into the appropriate cursor motion on the device's display. When the user releases the puck, the coupling between the puck and the cursor position is broken by the software, and hence, the cursor does not move backwards while the puck is being recentered.
While the device taught in the above-described patent application provides significant advantages over the dominant prior art solutions to the pointing device problem in the laptop marketplace, the device is less than optimum when used with a cell phone or other device with a relatively small screen. On a small screen, the ability to reposition the puck and then continue the motion in a manner analogous to that of mouse on a desktop computer is of limited value, since the amount of information available in the display is relatively limited, and hence, can be adequately accessed by a one-to-one mapping of the puck position to the position of the cursor on the screen.
On the other hand, the limited screen size places a premium on other operations such as scrolling. The small screen of a handheld device such as a cell phone can emulate a small window through which a much larger desktop is viewed. By moving the window in various directions, the desired portion of the desktop can be positioned under the window. Objects on the desktop under the window can then be selected by moving the cursor within the window. Hence, a pointing device for use in such an environment would benefit from having both a pointing function and a two-dimensional scrolling function.